<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <style>
        *{
            margin: 0;
            padding: 0;
        }
        button {
            width: 200px;
            height: 80px;
            background-color: #ccc;
            border: 1px solid #999;
            padding: 20px;
        }
    </style>
</head>
<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
    <button>按钮5</button>
    <script>
        var btns = document.querySelectorAll('button');
        for(var i =0;i<btns.length;i++){
            btns[i].onclick=function(){
                for(var j=0;j<btns.length;j++){
                    btns[j].style.backgroundColor='';
                }
                this.style.backgroundColor='red';
            }
        }
    </script>
</body>
</html>